When I installed the new version and afterwards i tried to look into the recycle bin … a total freez of my system was the result… Solution : old version reinstalled and everything went well… so i assume you got work tonight boys and girls … 
What is your system infomation? how did you uninstall the old version?
My system info is WINDOWS XP SP3 Zonealarm Free Firewall and I didn’t uninstall the old version : I just asked for an upgrade to 5.1 and so it happened…
with the old version I have no freezes no hassles … so I conclude that 5.1 is the culprit …
The problem was that when I tried to delete something ; the system froze completely and when I restarted my pc and I tried to look into the recycle bin ; bingo ! The same issue ! I use eraser for my recycle bin … maybe it doesn’t go along with 5.1 ???
Try a clean install with the new prerelease 5.1.874 and make sure that zonealarm has not blocked anything of avast, exclusions should be added to zonealarm for avast or any other security software you might have if you haven’t already.
I would tend to guess that ZoneAlarm might conflict with 5.1, and more specifically the behavior and web shields. This has to be verified of course.
Yes,me too. I installed the update yesterday and as soon as it restarted my PC also froze up. I had to boot into safe mode and remove it. I reinstalled Avast from the avast website and it worked until I restarted my computer. Froze again and I had to go into safe mode again and uninstall it. I ended up going back to AVG. I am using xp.
Same for me I have Zone Alarm so there might be the conflict using avira until this is sorted.
oh, I don’t have Zone Alarm.
New official release today, 5.1.889, try a manual program update from the avastUI.
I’ve used Avast for 9 years. Unfortunately this recent version conflicts with Zone Alarm on my Windows XP. Have finally had to uninstall and get AVG.
Over and out.